Electrically-heated steam generators



ELECTRICALLY-HEATED STEAM GENERATORS Filed Oct. 20, 1958 5 Sheets-Sheet l INVENTOR. WMTE/a TXVENDE F i HTTOENEY May 22, 1962 Filed Oct. 20, 1958 W. K. TAVENDER ELECTRICALLY-HEATED STEAM GENERATORS 3 Sheets-Sheet 2 WALTER H QE VENU /q BY HTTOENEY May 22, 1962 w. K. TAVENDER 3,036,195

ELECTRICALLY-HEATED STEAM GENERATORS Filed Oct. 20, 1958 3 Sheets-Sheet 3 i E. ,9 j l 2/: I I 21 23 v I 1 I I 12 fi W12 1/0.

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2 WALTER 14 H BY x25 31 12 HTTOENEY United States My present invention relates to electrically heated steam generators and comprises an improvement on the generator shown in the co-pending application of Reimers, Tavender and McCormick, Serial No. 335,574 filed February 6, 1953, now Patent No. 2,880,300 granted March 31, 1959.

The steam generators to which my invention is more particularly directed are of the type in which a small amount of water is maintained relative to the rate of evaporation and in which a pressure above atmospheric is maintained as, for example, a working pressure of about twenty five pounds above atmospheric, though this pressure may occasionally rise to fifty pounds. The generator must therefore be steam-tight and the admission of water must be closely controlled to maintain a constant level above the electric heater. This level control may be most satisfactorily attained by a float actuating a shaft that rotates with a minimum of friction so that the float may be responsive instantly and with precision to changes in the water level. The movements of the float are transmitted by a supporting arm to a rock shaft on which the arm is secured. The rock shaft offers no significant resistance to rotation so that the float rises and falls with the rise and fall of the water level with great precision and fidelity and slight changes in the water level are transmitted to the shaft.

The rotational movements of the shaft within the gen erator must be transmitted to a water level control which, for this purpose, is a sensitive electric switch in an electric control circuit. The electric control circuit controls a regulating valve in a water supply to the generator. Direct connection of the float shaft with the switch by ex tending the shaft through a steam-tight stuffing box in the wall of the generator would impair the sensitivity of the float or render it unreliable because the required tightness of the stufling box sufiicient to contain the high working pressures would introduce a frictional resistance of considerable and variable magnitude relative to the sensitivity of the float actuated rock shaft.

My present invention provides a steamtight coupling between the rock shaft within the steam generator and a switch controlling rock shaft outside the generator which is free from mechanical friction.

For this purpose the steam generator is fitted steamtightly with a closed, hollow, extension of nonmagnetic material co-axial with the float shaft and into which the shaft projects. The shaft is fitted with a magnet within the extension and the shaft and magnet are rotatable in the extension without friction.

The switch outside the steam generator is provided with a shaft co-axial with the float shaft and this switch shaft is provided with a magnet or magnetic element outside of the extension and within the magnetic field of the magnet on the float shaft so that the two shafts are coupled magnetically and without friction.

To provide against the possibility of an explosion by the accidental generation of a steam pressure sufficient to fracture the generator, the shell of the generator is so constructed that it will leak steam and water when a dangerous pressure is approached. For this purpose the wall or shell of the generator is made of two parts, one for water and the other for steam and is provided with complementary flanges'which are bolted or riveted together to make a steam-tight joint. These flanges, howflfice ever, yield sutficiently between the bolts or rivets to leak steam and water to relieve the pressure before a pressure suflicient to burst the generator is reached. Thus the halves may be made of a bronze casting tested at a pressure of 360 pounds per square inch, the flanged joints being leak proof at pounds pressure but yielding sufliciently to leak at about 200 pounds.

My invention is illustrated, by way of example, in the accompanying drawings, in which:

FIG. 1 is a side elevation of a steam generator embodying my invention, a part of an enclosure of the generator being removed,

FIG. 2 is an elevation of the right of FIG. 1, a part being broken away to show the electric heater and float.

FIG. 3 is a detail horizontal section on a larger scale of a portion of the generator showing the extension, the magnetic coupling and the electric switch, and,

FIG. 2 is a plan view, on a smaller scale, of the generator.

As shown in the drawings, a generator 11 embodying the invention is enclosed in a housing 10. The generator is supported in the housing 10 on a horizontal platform 10a mounted on upright standards 12, one at each vertical corner of the housing and by intermediate vertical beams 12]). The standards 12 also support a bottom or floor 12a of the housing. The platform 10a also carries the electric switch.

The steam generator 11 comprises an upper part 11:: and a lower part 11b having flanges 13 and 13a, respectively, by which the parts are secured steam-tightly by means of bolts 14 spaced about the flanges as shown in FIG. 4. The parts 11a and 11b are of hollow or cup shaped form and are extended sidewise as shown in FIGS. 2, 3 and 4 to provide a support for the float shaft and extension for the magnetic coupling. From the lower part of the generator water may be drained through a drain pipe, normally closed by a drain cock 15a.

Water to be vaporized is supplied from a supply line 31 entering the lower part of the housing 10. The supply of water is controlled by an electric solenoid valve 29, in turn controlled by the electric circuit, and the water thence passes through a rising pipe 30 to be delivered into the upper part of the generator. The pipe 30 is shown broken in FIG. 2 in order not to obscure the view of the generator.

Steam is delivered from the upper part of the generator through an outlet pipe 32 and control valve 16. A pressure gauge 35 is connected to the outlet pipe. A safety valve 33 is connected to the upper part of the generator by a pipe 34. The drain cock is mounted below the floor 120 of the housing and the steam control valve 16, the prmsure gauge 35 and the safety valve 33 are above the housing so that they are readily available for manipulation and observation.

A small quantity or" water to be vaporized is maintained in the lower part of the generator half 11!), the normal level of the water being indicated by the horizontal chain line in FIG. 2. Immersed in this water is an electric heater 18. The heater 18 is made of a closely coiled length of insulated heating conductor, 180, this conductor having a tubular shell of metal, preferably copper. The coil has a vertical axis and extends through the bottom of the generator steam-tightly to terminal connector ends 13a and 18b.

The heater 18 supplies a large quantity of heat relative to the amount of water in the generator thereby enabling the generator to be quickly started and stopped and to generate a large amount of steam for the size of the generator. To avoid exposing the heater or flooding the steam space, an accurate control of the water level generator taken from the 3 is required. This is obtained by a float 19 canried on an arm 119a fixed on a rock shaft 20 as shown in FIGS. 2 and 3. The rock shaft is mounted in bearings 2012 as indicated in FIG. 3 and rocks in these bearings with a minimum of friction. The rock shaft, in turn actuates a control switch in an electric circuit cont-rolling the solenoid valve 29.

To this end the shaft 20 is extended into a closed exshaft 20. This magnetic coupling involves no mechanical resistance or friction in the rotation of the shafts and'23.

A switch arm 190 is mounted in fixed position on the shaft 23 to rock with the shaft to open and close aswitch 24 in an electric circuit controlling the solenoid valve 29 and thus control the level of water' in the generator.

The above elements of the control serve to maintain a water level within close tolerances in the generator.

Should any part of the control become injured and inoperative and the water supply cut off, the electric heater would become exposed and might burn out. To avoid this a thermostat 26 is mounted in the generator adjacent the heater coils and is connected by a tube to an expansible disc control of the electric supply. The thermostat may be of a gas type or expansible liquid type set to operate at a safe temperature above the boiling point of the water under a selected pressure as, for example at a temperature of 275 F. This insures against burning out due to a failure of the water supply.

The above invention provides a steam generator in which steam may be generated in large quantity at pressures substantially above atmospheric in apparatus of limited volume safely and without attention by the user.

Having described our invention, we claim:

1. An electrically heated, steam generator for rapid evolution of steam under pressure which comprises a boiler having a water space and a steam space, said water space being smaller than said steam space, an electric heater'in said water space to rapidly vaporize said water, an extension from said steam space and sealed fluid-tightly therewith, said extension having a cylindrical wall of non-magnetic material, a shaft journaled in said steam space and extending into said extension centrally of said cylindrical wall, an arm fixed on said shaft, a float mounted on said arm and floating on water in said water space to rise and fail as the level of said water rises and falls thereby to rock said shaft, a permanent magnet secured on said shaft within the cylindrical wall of said extension, a second magnet mounted to rotate about the cylindrical wall of said extension and magnetically coupled with the permanent magnet on said shaft and an electric circuit to control the supply of water to said boiler and comprising a switch operated by said second magnet.

2. The steam generator of claim 1 in which said second magnet is an induction magnet.

References Cited in the file of this patent UNITED STATES PATENTS Garth May 12, 

